Heat sealing machine and method



June 28, 1955 N. LANGER 2,711,781

HEAT SEALING MACHINE AND METHOD Filed March 6, 1953 2 Sheets-Shea?l lQ15 17- Z3 N IN VEN TOR.

June 28, 1955 N. LANGER 2,711,781

HEAT SEALING MACHINE AND METHOD Filed March e, 195s INVENTOR.

2 Sheets-Sheet 2 Z, lijl .irme 28, lii

HEAT SEALHNG MACHINE AND METHOD Nicholas Langer, New York, N. Y..Application March 6, 1953, Serial No. 340,875

24 Claims. (Ci. 15442) This invention relates to the art of heatsealing, and, more particularly, to a machine and method of heat sealingor bonding layers or sheets of `thermoplastic material.

ln recent years various machines have been introduced for bondingtogether layers or plies of thermoplastic material by electrostaticheating of the material in a high frequency eld. The operation of thesemachines is based on passing the superposed plies of the thermoplasticmaterial through the space between a pair of electrodes connected to asource of radio frequency energy, the displacement of such plies beingeffected in a step-by-step or discontinuous manner, such as in aconventional sewing machine, or in a continuous manner, such as by measof a pair of feed rolls. T he powerful high frequency iield produced inthe electrode zone will heat up the plies of the material passingtherethrough to their bonding temperature, causing sealing or bonding ofsuch plies as a result of the joint eifect of heat and electrodepressure.

While electrostatic bonding machines of the described character,sometimes referred to in the industry as electronic sewing machines,have been used for some years on a rather limited scale, their use on alarge scale in the quantity production of articles formed fromthermoplastic sheet material was greatly handicapped and in many caseswas completely prevented by a combination of the following factors:

(l) The operation of conventional electronic sewing machines is based onthe heat produced in the material as a result of dielectric losses in ahigh frequency field. rthis introduces certain inherent limitations asto the types of thermoplastic materials which may be successfully bondedand obviously excludes such materials in which the dielectric losses arevery low. It so happens that there are various materials, such asparticularly polyethylene, which are characterized by an extremely lowloss factor, although they are quite desirable for other reasons, suchas low cost, high strength, chemical inertness, low gas permeability,and the like.

(2) In view of the extremely high frequencies used in electrostaticbonding machines, serious problems are introduced in connection withimpedance matching, in controlling the amount of heat generated in theplies, etc. Even very minute and frequently unavoidable variations inthe composition and thickness of the plies or in the rate feeding theplies past the electrodes may prevent the production of uniformly soundseals or bonds.

(3) The amount of high frequency energy required is quite considerableand the equipment for generating such energy is bulky and also expensiveto build and to operate. As a result, the initial cost of theseelectrostatic bonding machines is quite high and their commercial use isprofitable only in extreme cases where no other method of bonding willserve.

I have discovered that the outstanding problem may be solved and theforegoing disadvantages may be eliminated in a remarkably simple manner.

It is an object of the present invention to improve electronic bondingmachines.

It is another object of the present invention to provide a novel andimproved electronic bonding machine and method of the thermal impulsetype.

It is a further object of the present invention to provide a novelmachine and method for heat sealing or bonding together plies ofthermoplastic sheet material in which the sealing or bonding heat isgenerated by the contact resistance between a thin layer of electricallyconducting material and an electrode of relatively small surface area.

It is also within the contemplation of the invention to provide anelectronic bonding machine which does not require any high frequencycurrents for its operation but may directly be operated with alternatingcurrents of commercial power line frequency.

The invention also contemplates an electronic bonding machine which issimple and inexpensive to construct and to operate and which may bemaunfactured and sold at a fraction of the cost of conventional bondingmachines of the high frequency type.

Other and further objects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, in which:

Fig. 1 is a vertical sectional view, somewhat diagrammatic andfragmentary in character, of an electronic bonding machine embodying theprinciples of the invention;

Fig. 2 is a perspective view illustrating the operation of the machineshown in Fig. l in carrying out the method of the present invention;

Fig. 3 is a fragmentary top plan view of two layers of thermoplasticsheet material bonded together by the machine shown in Figs. l and 2;

Fig. 4 is a side elevational View, having parts in section, of amodified embodiment of the present invention;

Fig. 5 is a section taken on line 5-5 of Fig. 4;

Fig. 6 is a fragmentary top plan view of two layers of thermoplasticsheet material bonded together by the machine shown in Figs. 4 and 5;

Fig. 7 is a side elevational view, also diagrammatic and fragmentary incharacter and having parts in section of another modified embodiment ofthe present invention;

Fig. 8 is a section taken on line 8 8 of Fig. 7;

Fig. 9 is a fragmentary side elevation of a further embodiment of theinvention into an electronic bonding machine of the reciprocating type;

Fig. l0 is a front view of a portion of the machine shown in Fig. 9; and

Fig. ll is a fragmentary top plan view of two layers of thermoplasticsheet material bonded together by means of the apparatus shown in Figs.9 and 10.

Broadly considered, in accordance with the principles of my invention,the layers or plies of thermoplastic sheet material to be bondedtogether are brought into faceto-face superposed position and anelectrically conducting layer is placed thereon. This conducting layeris preferably constituted by a thin sheet of metal such as copper,aluminum, steel and the like although in many cases it is foundadvantageous to form the said layer of a metal having a relatively highspecific resistance and good resistance to oxidation such as stainlesssteel or a suitable nickel-chromium alloy known under the name Nichrome.An electrode of relatively small surface area in the form of a pointedrod or of a small wheel is brought into contact with the exposed surfaceof this metal layer and an electric current of suitable intensity ispassed through the circuit constituted by the electrode and the metallayer.

Due to the fact that the area of contact between the electrode and thethin metal layer is characterized by a relatively high resistance, uponcompletion of the electric circuit a considerable amount of heat will begenerated in such area. rl`his heat will be practically instantaneouslytransmitted through the thickness of the metal layer and will causeheating and bonding of the underlying thermoplastic layers in acorresponding area. To further promote and enhance this result, it isdesirable to form the electrode of a material of relatively highspecific resistance which is also capable of resisting the effect ofheat and oxidation. Carbon is a material which is excellently suited forthe purpose, preferably in the form of a compound of carbon or graphiteparticles with a suitable binder and in some cases a filler such as areused in the form of carbon brushes or for the purpose of electrodes inprimary cells, arc lamps, and the like.

Of course, the method described may be carried out in a great variety ofways and the metal layer and the electrode may be provided in the formmost suited for the particular method. Thus the electrode may be in theform of a pointed rod or wheel which may be reciprocated or rotated bysuitable apparatus and the metal layer may be in the form of a singleplate or in the form of an endless belt, as it will appear more fully asthe description proceeds. Also, the metal layer may be provided in theform of a layer of metal foil which is permanently bonded or laminatedwith one of the thermoplastic layers to be heat sealed to anotherthermoplastic layer.

Referring now more particularly to Fig. l of the drav ing, referencenumeral l0 denotes a working plate or base which may be formed of anysuitable material of an insulating or of an electrically conductingcharacter. In most cases, however, it is advantageous to form the saidbase in the form of a thick and smooth-surfaced layer of a suitableelastomer, such as silicone rubber. Upon base plate 10 are placed thetwo layers or sheets of thermoplastic material il and l2. A thin metallayer 14, such as a thin sheet of Nichrome having a thickness between0.001 and 0.005 is placed on the top surface of the thermoplasticlayers.

An electrode l5 in the form of a rod of metal, but preferably of carbon,has its pointed end applied with moderate pressure against a point orsmall area of the metal layer 14, and an electric current of suitableintensity is passed through the circuit constituted by the electrode andthe metal layer, including the area of contact between the said twoelements' denoted by numeral lo. As the current used is preferably oflow voltage and of high intensity, this is best accomplished byconnecting one end of the low voltage or secondary Winding 17 of astep-down transformer llS through a conductor f 19 to a metal cap orclamp 20 at the upper end of the electrode l5, while the other end ofthe said winding is connected through a similar conductor 2l to themetal layer ll, as indicated at 22. Preferably, conductors T19 and 2lare long and flexible enough to permit displacing the electrode over theentire exposed surface of metal layer le. Primary winding 23 oftransformer 1S is connected to a source of alternating current, such asthe usual 60 cycle power line through conductors 24 and 25.

From the foregoing description, the operation of this if simplestembodiment of the invention will be readily understood by those skilledin the art. Upon closing the primary circuit of the transformer, arelatively heavy current will be caused to now through the secondarycircuit constituted by secondary winding i7, conductors 19 and 21, metallayer 14 and electrode l5, such circuit obviously also including thearea of contact between the metal layer and the electrode indicated at16. Since the electrical resistance of the contact area is relativelyhigh, a considerable amount of heat will be generated r therein. Thisheat will be practically instantaneously transmitted through thethickness of metal layer 14 and will cause heating of the directlyunderlying thermoplastic layers in an area 26 which is in exactcorrespondence with the contact area although it may be slightly largerdue lil to the fact that the heat will spread to a moderate eX- tent inthe metal layer, depending on the thermal conductivity thereof and uponthe speed with which the entire operation is carried out. As a result ofthe cornbined effect of heat and contact pressure, the thermoplasticlayers will be bonded together in the heated area.

The operation of the machine, as just described, will produce a heatseal or bond in a single small area. In most cases, of course, sealingor bonding over a substantial continuous or discontinuous linear area orreg lcsired. ri`his may be accomplished by maintaining the circuitclosed and displacing the electrode over and in contact with the metallayer at a moderate speed. lt viii be found that the thermoplasticlayers will be fused or bonded together in exact correspondence with thepati described by the electrode point upon the exposed surface of tnemetal layer. This mode of opera* tion wiil be best understood from Fig.2 in which similar reference numerals have been used to denotecorrespending parts. it will be noted that by displacing the point ofelectrode l5 on metal layer ld along a sinuous path 27, the underlyingthermoplastic layers will be heat sealed or bonded together along acorresponding path. Obviously, the apparatus and method just describedpermit the production of a bond between two or more layers ofthermoplastic material along any desired configuration. In general, anypattern, however complex, may be formed without the slightestdih'iculty, including patterns which may cross over each other anynumber of times. Fig. 3 illustrates by way of example a pair ofthermoplastic sheets ll and l2 bonded together in accordance with thepattern Z7 shown in Fig. 2.

The modified embodiment of the invention shown in Figs. 4 and 5 of thedrawing is provided for the continuous formation of a linear bond orseam in layers of thermoplastic material at a high rate of speed. lnthese figures, reference numerals il and 42 denote a pair of rolls ordrums between which there is tensioned an endless belt 43 of thin metal,such as Nichrome, stainless steel and the like. Numerals d4 and 45denote another pair of similar rolls between which is tensioned anotherendless belt 46 of flexible sheet material. Belt 46 may also be formedof metal although in many cases it is preferred to make this belt ofsilicone rubber or of some other elastomer which has good surfaceadherence to the thermoplastic layers to be bonded together. Belts d3and 4d are arranged in closely spaced parallel relation with respect toeach other so that when a pair of superposed thermoplastic layers i7 andare introduced therebetween and rolls di, 42 and rolls 44, 45 arerotated by any suitable means (not shown) in opposite directions, thethermoplastic Vlayers will be continuously advanced thereby in thedirection of arrow A narrow sealing roll or wheel 50 is pressed againstthe top surface of metal belt 43 while a pressure roll 5l is applied inrolling contact with the lower surface of belt 46 so that thethicknesses of belt 43, thermoplastic layers 47 and 48 and of belt doare caused to pass through the bight of the said rolls. 'She system isenergized by connecting primary winding 52 of a stepdown transformer 53to a source of alternating current 54. The secondary or low-voltagewinding 5S of the said transformer has its ends connected to rolls 50and 42 through conductors 56 and 57, respectively.

During operation of the machine, rolls el, d2 and lil/, t5 are rotatedin opposite directions by any suitable mechanism, causing concurrentdisplacement of belts i3 and 46, with thermoplastic layers d'7 and i3therebetween, through the bght of sealing wheel or roll 50 and pressureroll 5l. As the primary winding of transformer 53 is energized fromalternating current source 5d, a heavy current will be caused to flowthrough the secondary cir cuit comprising secondary windinfY conductors56 and 57, rolls Sil and 42, and the portion of endless metal belt i3interposed between said rolls. Most of the heating elect of thesecondary current will be concentrated in the area of contact betweensealing wheel or roll 5l) and the upper surface of belt 45 due to thefact that the resistance of the circuit is the highest in thatparticular area. To further increase the resistance in that area, it ispreferred to provide the sealing wheel with a relatively narrowcircumferential face, as this will best appear in Fig. 5 and to form thesaid wheel of a material of relatively high specic resistance, such ascarbon or graphite.

The heat generated in the area of contact is quickly transformed byconduction through the moderate thickness of metal belt 43, causing heatsealing of the underlying thermoplastic layers 47 and 48, as a result ofthe combined eilect of sealing heat generated therein and of thepressure applied thereto by rolls 5t) and Si. As new portions 0f thethermoplastic layers are continuously passed through the sealing stationconstituted by the bight of rolls 5t) and 5l, a longitudinal sealedregion or seam 5S will be formed in the layers as this will be readilyobserved in Fig. 6.

The modified embodiment of the invention shown in Figs. 7 and 8 is inmany respects similar to the one just described except for the factthat, instead of an endless metal belt, a continuous length of thinmetal foil is ernployed, equaling in length that of the thermoplasticlayers to be bonded. This form of bonding apparatus essentiallycomprises a sealing wheel or roll 7l and a pressure roll 72 mounted forrotation in cooperating relation. A thin narrow strip or band 73 ofmetal foil, such as aluminum, copper, steel, and the like, is unwoundfrom a supply roll '74 and is by means of a guide roll 75 and feed table76 passed through the bight of rolls 71 and 72 together with underlyingthermoplastic layers 7i? and Sil. As it will be best observed in Fig. 8,sealing wheel or roll 7l is relatively narrow and is formed of carbon,while rolls or wheels 77 and 7S, one at each side of the sealing wheel,are formed of an elastomer, such as silicone rubber. The yieldingcharacter of rolls 77 and 78 will assure that metal foil 73 and theunderlying thermoplastic layers '79, Sil will be positively guided inrolling contact with the pressure roll 72 while at the same time thecircumferential surface of sealing roll 71 will be iirmly pressedagainst the top surface of the layer of metal foil 73.

The electrical circuit of this modified embodiment of the inventioncomprises a step-down transformer 1 of which the primary winding 32 isconnected to a source of alternating current 83. The secondary circuitcomprises secondary winding Se of the transformer, conductors 85 and 86,respectively connecting the ends of the secondary winding to sealingroll 7l and guide roll 75, and the portion of metal foil 73 interposedbetween the said walls. The secondary circuit is closed in itself and asmost of its resistance is concentrated in the area of Contact betweensealing roll 71 and metal foil '73, as indicated at 87, a considerableamount of heat will be generated in said area. This heat will betransmitted by conduction through the thickness of metal foil 73,causing heat sealing of the underlying thermoplastic layers 79 and Si)in a corresponding area as a result of the combined eiect of sealingheat and of the pressure prevailing between rolls 71 and 72.

Rotation of rolls 7l and 72 in opposite directions by any suitablemechanism (not shown), will progressively bring new portions of metalfoil 73 in combination with underlying thermoplastic layers 79 and 8uinto the sealing station constituted by the bight of rolls 71 and 72.Thus, a continuous longitudinal seam will be formed in the thermoplasticlayers, similar to seam S8 shown in Fig. 6. After the sealing operation,the metal foil 73 covering the seam may be stripped oil, if desired.Since the metal foil is preferably used only once, it is desirable touse a foil of such material and gauge as to keep the cost of thisexpendable element at a minimum. In this connection, however, it is tobe noted that it is entirely feasible to roll u'p the metal foil afterit has passed through the bight of rolls 71 and 72 and to reuse the samelength of foil a number of times.

Fl`he principles of the present invention are particularly suitable forthe construction of bonding machines wherein the layers to be bonded aredisplaced in a step-by-step or discontinuous manner, much in the sameway as is the case in a conventional sewing machine. A bonding machineof this general type is shown in Figs. 9 and l0.

`eferring now more particularly to Figs. 9 and l() of 'he referencenumeral @il denotes the head of suitable reciprocating mech nism, suchas the one `und in conventional sewing machines. rihis mecha- .ismactuates a reciprocating bar gl and a pressure foot 2 i predeterminedsequence, the said pressure foot cop ing with a feed dog 53 to advancethe layers t t' errnop istie material interposed therebetween. w o hefact that the reciprocating mechanism and its cooperation with a bar,pressure foot and feed dog are well known to those skilled in the art,no detailed description thereof will be necessary.

r"he lower end of reciprocating bar 9i carries a metal to axial recessthis der there is inserted an eL ctrode 97 in the form of a pointedcylindrical rod which is fixed in the holder by ca o'-c a set screw *twill be noted that elecrode 91 and its holder 9G are electricallyinsulated from rest of reciprocating bar 9i by the interposition of ieeeof insulating material 99. Electrode $7 may be Tred of any suitablematerial having good mechani- -rl i ngth, a relcnvely high specicresistance and good fe to oxidation. Carbon, graphite, tungsten c-r t.num are quite satisfactory r the purpose al- H other conductingmaterials, not excluding metals ol high conductivity, such as silver, orsilver alloys.

Pressure foot @2 comprises a rigid metal frame .lt-ii), to which thereis welded or otherwise secured a thin layer of metal lill. This may beformed o iii-chronic, stainless steel, tunasten, molybdenum, or thelille. Metal layer is insulated from the reciprocating mechanism by theinterposition of piece of an electrical insulating material in itsactuating rod H33.

The top or operating surface of feed dog 93 is covered with a layer of asuitable elastomer, such as of silicone rubber, constituting a pressuremember, the working face of which is arranged for cooperation with thelower face of metal layer lill and as a result of its st lrfacecharacteristics is adapted for fricional engagement with the lower oneof layers 9d and E of the 1h cplasric sheet material.

Lhe electrical system of the iachine comprises a stepdown t .sformerlbi, having a primary or high volt- '1g l-Q a secondary or low volta@eThe ends or" secondary winding M57 are retively connected to electrode97 and frame i6@ carn'ietal layer through lead wires ldd an if throughexible conductors il@ and ill so that such electrical col nection ismaintained during the reciprocalion of electrode 97 and of pressure footZ.

The primary winding ldd of transformer has one of its ends directlyconnected to terminal il?. and its other end is connected to terminal133 of a source of alter-hating current of comr -cial power linefrequency through a Atime delay switch rheostat lid, and an onch le.Actuating plunger M7 of time delay switch is operable by means ofactuating rod r3.8, mounted on the upper portion of reciprocating barThe time when operation of the time delay switch is initiated duringdownward displacement of recipocating bar l is adjustable by means ofset screw epending from the end of actuating rod M8 and the cngth of theperiod after which the said switch is auto. matically disabled or openedis adjustable by means of screw 120. In View of the fact that time delayswitches new "we of various types adaptable to the purposes of thepresent invention are well known to those skilled is the art, the saidswitch has been merely diagrammatically indicated in the drawing. For adetailed description or such switches reference may be had, for example,to my Patents 2,460.46() and 2,479,375.

From the foregoing description, the operation of the bonding machine ofthe invention will be readily understood by those skilled in the art.

When beginning Vthe bonding operation, the layers @si and 95 or" tirethermoplastic sheet material to be not together are placed inace-to-face position on layer of feed dog 93 and pressure foot 92 ismanually set into its operative position, holding the said layerscon'lned or compressed between metal layer lill and elastic layer Thebonding machine is now ready tor automatic operation by actuating thedriving I, pressure foot g2 and feed dog 23 are operated properly timedsequence in a rrauner similar to the operation oi a conventionalpower-driven sewing machine. During this automatic operation, thefollowing steps are carried out cyclically and in very rapid succession:

l. Pressure foot 91?. is lowered to conne thermoplastic layers and 95between metal layer lill surface lof-f of feed dog 2. -Reciprocating bar*3l is lowered, thereby pressing the pointed end of electrode 97 againstthe upper surface of metal layer Lilli carried by frame 19d of thepressure foot. completes the secondary circuit of the transformer.

3. Shortly before, coincidentally with, or preferably immediately afterelectr-ode 97 has reached its contacting and pressure applying positionwith respect to metal layer lill, set screw il? will be displaceddowntyardly by means of actuating rod S, concurrently with the downwarddisplacement of reciprocating rod 91 and the said set screw will strikeagainst actuating plunger Ill?" oi time delay switch ld.

Operation of the time delay switch illiis initiated, the said s. itchbeing oi the type which closes an electric circuit at once and opens thesaid circuit automatically, after a pr determined and adjustable timedelay period.

5. The primary circuit, including terminal il?, of the alternatingcurrent power line, main switch llo, time delay switch lift, rheostatM5, primary winding lilo, terminal i12 of the power line is nowenergized. This will induce a low-voltage, high-intensity current in thesecondary circuit comprising secondary winding fit-97, conductors i953,69, lli?, lll, electrode 97 and metal layer lill, i' sing the relativelysmall area oi Contact between the pointed end oi said electrode and thesurtace of said metal layer.

6. The heavy current owing through the secondary circuit will quicklyheat the said area of Contact to a relatively high ltemperature due tothe fact that most of the resistance of the circuit is concentrated insaid area. This temperature is reached practically instantaneously, dueto the very low heat capacity of the thin metal layer in the contactarea. The heat thus produced is rapidly conducted through the thicknessol metal layer lill into a corresponding region of the underlyingthermoplastic layers 9d and 95. As a result of the combined effect ofthe heat and pressure, a stitch is formed in the said region, this termbeing intended to mean a unitary area or spot wherein the thermoplasticlayers are permanently bonded or fused together.

7. Immediately upon the said stitch being cornpleted, the time delayswitch lili will automatically open the primary circuit and thus willalso deenergize the secondary circuit. However, the pressure of metallayer lill on the stitch is maintained for a short predetermined periodthereafter, in order to permit the stitch to cool and to consolidateunder pressure, thereby developing the full strength of the bond.

8. Reciprocating rod 91:1 is now raised, lifting up electrode 97 frommetal layer lill.

9. Feed dog $3 is actuated, its operative surface 194 engaging with somefriction the lower face of thermoplastic layer 95, thereby advancing anew length of layers 94 and 9S into stitchforming position, whereuponthe entire cycle is repeated over and over again so long as the machineis maintained in operation and is supplied with films of thermoplasticmaterial.

Fig. ll shows the thermoplastic layers 94 and 95 bonded together by thereciprocatory bonding machine of the invention. lt will be noted thatthe external appearance ot the bonded product is not unlike to that of apair of layers stitched together by means of a conventional sewingmachine. However, the actual bond between the layers is formed by fusionof the layers in uniformly spaced individual areas 121 and not by thelocking effect of a thread. While in Fig. 1l the line of fusion bond isin the form of a succession of spaced stitches, such unit lengths offusion bond is the form of succession of spaced stitches, such ogtus olfusion bond may be caused to merge into each other by appropriatecontrol of the bonding cycle, particularly by making the unit length bywhich the materials are advanced after each stitch less than the lengththat is bonded together during each bonding cycle. This will cause thesuccessive stitches to overlap and to merge int-o each other. To furtherfacilitate this merging etlect, it is in some cases advantageous toreplace the pointed electrode with an electrode having a wedge-shapedend, the width of the wedge being arranged in the direction in which thethermoplastic layers to be bonded are displaced.

The machines and methods of the invention are suitable for bondinglayers of all types of thermoplastic material, such as Piiolm (rubberhydrochloride),

. Vinylite (a copolymer of vinyl chloride and vinyl acetate), Polythene(polyethylene), Saran (vinylidene chloride), and the like. While theinvention has been described and ill strated with particular referenceto bonding together two plies of thermoplastic material, they areobviously applicable with equal or similar results to the bonding ofthree or more plies of such materials.

What is claimed is:

l. The method of heat sealing layers of thermoplastic material whichcomprises coniining the thermoplastic loyers etween one surface of anelectrically conducting layer and a backing surface, applying anelectrode to a small area oiE the other surface of said conductinglayer, and passing electric current through the circuit constituted bysaid electrode and the conducting layer to cause the generation orsealing heat in the area of contact without the generation of sealingbeat in the remainder of said conducting layer thereby to ei'lect heatscaling of the underlying thermoplastic layers in a corresponding areaby said sealing heat transmitted from sa d area of contact to saidthermoplastic layers through the thickness of said conducting layer.

2. The method or heat sealing layers of thermoplastic material whichcomprises coniining the thermoplastic layers between one surface of ametal layer and a npking surface, applying an electrode to a relativelysmall area of the other surface of said metal layer, and providing adifference in electric potential between said electrode and said metallayer thereby to cause current to flow through the area of contact andheat sealing of the underlying thermoplastic layers in a correspondingarea as a result or the heat generated in said area oi Contact andtransmitted from said area of Contact to said thermoplastic layersthrough the thickness of said metal layer while the remainder of saidmetal layer is monetair-.ed below heat sealing temperatures.

3. The method of heat sealing layers of thermoplastic material whichcomprises superposing an electrically conducting layer on thethermoplastic layers, applying an electrode to a small area of theexposed surface of said conducting layer, and passing electric currentthrough the circuit constituted by said electrode and the conductinglayer thereby to heat the area of contact therebetween and heat sealingof the underlying thermoplastic layers in a corresponding area by heattransmitted from said area of Contact to the thermoplastic layersthrough the thickness of conducting layer while maintaining theremainder of said conducting layer below heat sealing temperatures.

4. The method of heat sealing layers of thermoplastic material whichcomprises superposing metal layer on the thermoplastic layers, bringingan electrode of small area into contact with the surface of the metallayer, and causing relative displacement of said electrode with respectto said metal layer while passing an electric current through the areaof contact thereby sequentially causing the generation of heat in thepath described by the area of Contact of said electrode and heat sealingof the underlying tnermoplastic layers along a corresponding path byheat transmitted from said area of contact to the thermoplastic layersthrough the thiclo ness or said metal layer while the remaincer of saidmetal layer below heat scalinfy temperatures.

5. The method of heat sealing layers of thermoplastic material whichcomprises interposing the thermoplastic layers between a relatively thinmetal layer and a layer of backing material, bringing an electrode ofsmall area and having an electrical conductivity lower than that of saidmetal layer in pressure Contact with the exposed surface of said metallayer, and displacinfy the area of contact while passing an electriccurrent through said area thereby sequentially. causing the generationof heat in the path described by said displaced area and heat sealing ofthe underlying thermoplastic layers along a corresponding path by heattransmitted from said area of Contact to the thermoplastic layersthrough the thickness of said metal layer while maintaining theremainder of said metal layer below heat sealing temperatures.

6. The method of heat sealing layers of thermoplastic material whichcomprises interposing the thermoplastic layers between a tlexible metallayer and an elastic backing layer, bringing an electrode ot small areainto pressure contact with the surface of the metal layer, and causingrelative displacement of said electrode with respect to said metal layerwhile passing an electric current through the area of contact therebysequentially causing the generation of heat in the path described by thearea of contact of said electrode and heat sealing of the underlyingthermoplastic layers along a corresponding path by heat transmitted fromsaid area of Contact to said thermoplastic layers through the thicknessof said metal layer while maintaining the remainder of said metal layerbelow heat sealing temperatures.

7. The method of heat sealing layers of thermoplastic material whichcomprises interposing the thermoplastic layers between a metal layer andbacking layer, bringing an electrode oi small area into Contact with thesurface ot the metal layer, producing relative displacement of saidelectrode with respect to said metal layer while passing an electriccurrent through the area of Contact thereby sequentially generating heatin the path described by the area of contact of said electrode and heatsealing of the underlying thermoplastic layers along a correspondingpath by heat transmitted from said area ot contact to said thermoplasticlayers through the thickness of said metal layer while maintaining theremainder of said metal layer below heat sealing temperatures, and thenseparating the heat sealed thermoplastic layers from said metal layerand said backing layer.

8. The method of heat sealing layers of thermoplastic material at leastone of which has a thin layer of metal permanently bonded thereto whichcomprises bringing the thermoplastic layers into ace-to-face Superposedposition with the metal layer exposed; bringing an electrode ofrelatively small area into contact with the exposed surface of the metallayer, and causing relative displacement of said electrode with respectto said metal layer while passinfy an electric current through the areaof contact thereby sequentially generating heat in the path described bythe area of contact of said electrode and heat sealing of the underlyingthermoplastic layers along a corresponding path by heat transmitted fromsaid area of contact to said thermoplastic layers through the thicknessof said metal layer while maintaining the remainder of said metal layerbelow heat sealing temperatures.

9. The method of heat sealing layers of thermoplastic material whichcomprises continuously displacing the thermoplastic layers incombination with a superposed metal layer through a sealing stationconstituted by an electrode surface of small area and a backing surfaceso that the electrode is in contact with said metal layer, passing anelectric current through the area of contact thereby sequentiallygenerating heat in the path described by the area of contact of saidelectrode and heat sealing the underlying thermoplastic layers along acorresponding path by heat transmitted from said area of contact to saidthermoplastic layers through the thickness of said metal layer whilemaintaining the remainder of said metal layer below heat sealingtemperatures, and

"\ then separating said metal layer from the heat sealed thermoplasticlayers.

l0. The method of heat sealing layers ci thermoplastic material whichcomprises superposing a metal layer upon the thermoplastic layers,displacing the superposed layers throt h the bight of an electrode rolland a pressure roll with the circumferential surface of said electroderoll in rolling pressure Contact with the exposed surface ot' the metallayer, passing an electric current through the area ot contact therebysequentially causing the generation of heat in the path described by thearea ot contact of said electrode roll and heat sealing of theunderlying thermoplastic layers along a corresponding path by heattransmitted from said area of contact to said thermoplastic layersthrough the thickness of said metal layer while maintaining theremainder of said metal layer below heat sealing temperatures, andcontinuously separating said metal layer from the heat sealedthermoplastic layers.

ll. The method of heat sealing layers of thermoplastic material whichcomprises displacing the thermoplastic layers in combination with a thinmetal layer, bringing an electrode of small area into transientreciprocatory contact with the exposed surface of the metal layer duringsuch displacement, and passing an electric current through the circuitconstituted by said electrode and said metal layer during at least aportion of the period while said circuit is closed thereby to cause thegeneration of heat in the area of Contact and the formation of spacedbonded areas in the thermoplastic layers by heat transmitted from saidarea of contact to said thermoplastic layers through the thickness ofsaid metal layer while maintaining the remainder of said metal layerbelow heat sealing temperatures.

l2. T he method of heat sealing layers of thermoplastic material whichcomprises displacing the thermoplastic layers 'with respect to a thinmetal layer, bringing an electrode of small area into transientreciprocatory contact with the exposed surface of the metal layer duringsuch displacement, and passing an electric current through the area ofcontact during at least portion oi the period while such contact existsthereby to cause the practically instantaneous generation of heat in theaea of contact and the formation of spaced stitch-simulating bondedareas in the underlying thermoplastic layers by heat transmitted fromsaid area of contact to said thermoplastic layers through the thicknessof said l l metal layer While maintaining the remainder of said metallayer below heat sealing temperatures.

13. The method of heat sealing layers of thermoplastic material whichcomprises conning a linear region of limited length of the layersbetween a thin metal layer and a backing layer, bringing an electrode ofsmall area into Contact with the exposed surface of the metal layer,passing an electric current through the area of contact during at leasta portion of the period while such contact exists thereby to cause thepractically instantaneous generation of heat in lthe area of contact andthe forma tion of a corresponding stitch-simulating bonded aren in thethermoplastic layers by heat transmitted from said area of contact tosaid thermoplastic layers through the thickness of said metal layerwhile maintaining the remainder of said metal layer below heat sealingtern peratures, and then advancing a new region of the thermoplasticlayers into conned relation with said metal and backing layers andrepeating thereon the same procedure.

i4. The method of heat sealing layers of thermoplastic material whichcomprises compressing a linear region of limited length of the layersbetween a thin metal layer and a backing layer, bringing an electrode ofsmall area into Contact with the exposed surface of the metal layer,passing a pulse of electric current through the circuit constituted bysaid electrode and said metal layer thereby to cause the generation ofheat in the area or" Contact and bonding oi the thermoplastic layers ina corresponding area by heat transmitted from said area of contact tosaid thermoplastic layers through the thickness of said metal layerWhile maintaining the remainder of said metal layer below heat sealingtemperatures, maintaining the co-; pression on said area after the endof said pulse for a period suil'lcient to have the bonded area toconsolidate, and then discontinuing said compression and advancing a newregion of the thermoplastic layers into cooperating relation with saidmetal and backing layers.

l5. A machine for heat sealing layers of thermoplastic materialcomprising, in combination, a thin metal layer and a backing layerbetween which the thermoplastic layers may be compressed, an electrodeof small arca adapted to be brought into contact with said metal layer,and means for passing an electric current through the circuitconstituted by said electrode and said metal layer, the respectiveelectrical resistances of said circuit constituents being so determinedas to Cause the generation of sealing heat solely said area of contactheat sealing of the thermoplastic layers in a corresponding area by heattransmitted from said area of Contact to said thermoplastic layersthrough the thickness oi said metal layer.

le. A ma e for heat sealing layers of thermoplastic material comprising,in combination, a thin metal plate and a backing plate between which thethermoplastic layers may be interposed, an electrode of small areaadapted to be brought into Contact with a restricted area of the exposedsurface of the metal plate, means for causing relative displacement oisaid electrode With respect to said metal plate, and means for passingan electric current through the circuit constituted by said metal plateand said electrode including said area ci contact during saiddisplacement, the respective electrical resistances of said circuitconstituents being so determined as to cause the generation o'r` sealingheat solely in said area of contact and heat scaling of thethermoplastic layers in a corresponding area by heat transmitted fromsaid area of contact to said thermoplastic layers through the thicknessof said metal plate.

i7. A machine for heat sealing layers of thermoplastic materialcomprising, in combination, a thin metal plate and a backing platebetween which the thermoplastic layers may be interposed, an electrodeof small area and having an electrical conductivity substantially lowerthan that of said metal plate adapted to be brought into pressurecontact with a restricted area of the exposed surface of the metalplate, means for causing relative displacement of said electrode and ofsaid metal plate with respect to each other, and means for passing anelectric current through said area of contact thereby sequentiallycausing the generation of sealing heat solely in the path described bysaid displaced area of contact and heat sealing of the thermoplasticlayers a corresponding path by heat transmitted from said. area otcontact to said thermoplastic layers through the thickness or" saidmetal plate.

A machine for heat sealing layers of thermoplastic material comprising,in combination, an electrode roll and a pressure roll, means fordisplacing the thermoplastic layers to be sealed in combination with asuperposed thin metal layer through the bight of said rolls with theelectrede roll in contact with the exposed surface of the metal layer,and means for passing an electric current through the a. of contactthereby to generate sealing heat solely in said area and to continuouslyheat seal the thermoplastic layers along the path described by said areaby heat transmitte" rrom said area of contact to said thermoplasticlayers through the thickness or" said metal layer.

ble metal through the bight oi said rolls in contact with thecircumference of said electrode roll, means for displacing thethermoplastic layers in contact with sai metal belt said pressure roll,and a source of electric current connected between said electrode rolland said metal belt to cause current to flow through and the generationor sealing heat solely in the area of Contact and heat sealing of thethermoplastic layers in a path corresponding to the displacement of saidarea by heat transmitted from said area ol contact to said thermoplasticlayers throuh the thickness of said metal belt.

20. A macl for heat sealing layers of thermoplastic material comprising,in combination, an electrode roll and a pressure roll, means forcontinuously feeding the layers to be sealed in combination with asuperposed thin and exible metal layer thro "h the bight of said rollsso as to have the circumferential surface of the electrode roll in rcing pressure contact with the exposed surface of the metal layer, andmeans for passing an electric current through the area of contractbetween said electrode roll and said metal layer thereby to cause thegeneration of sealing heat solely in such area and the continuousformation of a longitudinal seam in the underlying thermoplastic layersas a result of said sealing heat being transmitted from said area ofcontact to said thermoplastic layers through the thickness of said metallayer.

2l. A machine tor heat sealing layers of thermoplastic materialcomprising, combination, an electrode roll having a relatively smallcircumferential surface and a pressure roll, a feeding and guidingmechanism for continuously displac g the thermoplastic layers to besealed in combination with a superposed strip of metal foil through thebight of said rolls so as to have the circumferential surface theelectrode in rolling pressure contact with the exposed surface ol themetal foil, and means for passing an elect i current through the circuitconstituted by said electrode roll and a portion of said foil includingthe continuously displaced area of Contact therebetween thereby to causethe generation of sealing heat solely in sch area and the progressiveformation of a longitudinal seam the underlying thermoplastic layers asa result of said sealing heat being transmitted from said area oiContact to said thermoplastic layers through the thickness of said metalfoil.

22. A machine cr heat sealing layers oi thermoplastic materialcomprising i combustion, an electrode member and a pressure memberincluding metal layer, means for causing relative reciprocation of saidmembers to periodically bring seid electrode contact with one face of 13said metal layer, means for progressively feeding the layers to be heatsealed into contacting relation with the other face of said metal layer,an actuating mechanism for said reciprocating means and for said feedingmeans to progressively advance further lengths of said thermoplasticlayers into cooperating relation with said metal layer, a circuit forpassing an electric current through the area of contact ot saidelectrode and said metal layer, and a switching mechanism operable intimed relation with the operation of said actuating mechanism forclosing said i circuit during at least a portion of the period whilesaid electrode is in contact with said metal layer- Athereby to causethe generation of sealing 1neat solely in the area of contact and heatsealing of the underlying thermoplastic layers in a corresponding areaby transmission of said sealing heat from said area of contact to saidthermoplastic layers through the thickness of said metal layer.

23. A machine for heat sealing layers of thermoplastic materialcomprising, in combination, an electrode 1nember, a pressure membercomprising a metal layer, means for reciprocating said members toperiodically bring said electrode member into contact with one face ofsaid metal layer, means for discontinuously advancing the layers to beheat sealed into contacting relation with the other face of said metallayer, an energizing circuit including a switch adapted when actuated topass heating current through the area of contact between said electrodemember and said metal layer, and an actuating mechanism for operatingsaid reciprocating means, said advancing means and said switching meansin such predetermined sequence as to progressively advance further unitlengths of said thermoplastic layers into sealing relation with saidmetal layer and to cause heat sealing of such unit lengths by thesealing heat generated solely in the area of contact between saidelectrode member and said metal layer and transmitted from said area ofcontact to said thermoplastic layers through the thickness of said metallayer.

24. A machine for heat sealing plies of thermoplastic materialcomprising, in combination, a first pressure member comprising anelectrode, a second pressure member comprising a metal layer mounted forcooperation therewith, means for reciprocating said members foralternately bringing said electrode into contacting relation with oneface of said metal layer and to apply pressure upon a pair of plies ofthermoplastic material by the other face of said metal layer, aswitching mechanism operable in the pressure-applying position of saidmembers to interpose said electrode and said metal layer into anelectrical circuit for a predetermined period thereby to cause thegeneration of sealing heat solely in the area of contact between saidelectrode and one face of said metal layer and bonding of the plies thatare in pressure contact with the other face of said metal layer in acorresponding area by heat transmitted from said area of contact to saidplies through the thickness of said metal layer, feeding means operableafter the end of said period for discontinuously advancing further unitlengths of the plies into cooperating relation with said members, and anoperating mechanism for actuating said reciprocating means, saidswitching mechanism and said feeding means in such predeterminedsequence that the period of pressure application upon said plies extendsbeyond the period of heat application to such plies.

References Cited in the le of this patent UNITED STATES PATENTS2,302,024 Goss Nov. 17, 1942 2,525,356 Hoyler Oct. 10, 1950 2,556,008Spalding June 5, 1951 2,589,777 Collins Mar. 18, 1952 2,627,893 WilliamsFeb. 10, 1953 2,633,443 Langer Mar. 31, 1953 2,640,488 Welch June 2,1953 2,640,798 Langer June 2, 1953

15. A MACHINE FOR HEAT SEALING LAYERS OF THERMOPLASTIC MATERIALCOMPRISING, IN COMBINATION, A THIN METAL LAYER AND A BACKING LAYERBETWEEN WHICH THE THERMOPLASTIC LAYERS MAY BE COMPRESSED, AN ELECTRODEOF SMALL AREA ADAPTED TO BE BROUGHT INTO CONTACT WITH SAID METAL LAYER,AND MEANS FOR PASSING AN ELECTRIC CURRENT THROUGH THE CIRCUITCONSTITUTED BY SAID ELECTRODE AND SAID METAL LAYER, THE RESPECTIVEELECTRICAL RESISTANCES OF SAID CIRCUIT CONSTITUENTS BEING SO DETERMINEDAS TO CAUSE THE GENERATION OF SEALING HEAT SOLELY IN SAID AREA OFCONTACT AND HEAT SEALING OF THE THERMOPLASTIC LAYERS IN A CORRESPONDINGAREA BY HEAT TRANSMITTED FROM SAID AREA OF CONTACT TO SAID THERMOPLASTICLAYERS THROUGH THE THICKNESS OF SAID METAL LAYER.